The effects of using two varieties of one language on cognition

Although the question of whether and how bilingualism affects executive functions has been extensively debated, less attention has been paid to the cognitive abilities of speakers of different varieties of the same language, in linguistic situations such as bidialectalism and diglossia. Similarly to the bilingual situation, in bidialectalism and diglossia speakers have two language varieties that are active at the same time. However, these situations have been argued to potentially provide varied, and possibly fewer, opportunities for mixing or switching between the varieties, which may in turn lead to different cognitive outcomes than those reported in bilingualism. Here we review the available evidence on the effects of bidialectalism and diglossia on cognition, and evaluate it in relation to theories of the effects of bilingualism on cognition. We conclude that investigations of bilingualism, bidialectalism and diglossia must take into account the conversational context and, in particular, the opportunities for language switching that this affords.